Meta S. Brown

The Tolerance of Gossypium hirsutum for Deficiencies and Duplications

Exposure of germinating seeds of G. hirsutum to 1200r of X-rays was effective in producing chromosome aberrations. Ten lines having 12 different translocation complexes were recovered, involving a minimum of 29 breaks and rearrangements. At least ten, and probably all twelve, of these complexes gave one or more viable and fertile deficiency-duplication genotypes when outcrossed. Several of the complexes differed in the size of the chromosomes and length of the interchanged arms in such a way as to permit identification of the heterozygote and some or all of the deficiency-duplications by the configurations formed at metaphase I. In three lines, deficiency-duplications for segments carrying marker genes were recovered. It is concluded that the recovery of viable, fertile deficiency-duplications from translocations is the rule rather than the exception in this amphidiploid species.

Attributes of Intra- and Interspecific Aneuploidy in Gossypium

The genus Gossypium is favourable material for the recovery and study of aneuploids, as it includes allotetraploids which readily tolerate duplications and deficiencies, and a series of diploids which can be combined with tetraploids to make allohexaploids. The latter provide a further source of aneuploids, especially trisomics involving diploid genomes with different degrees of relationship to G. hirsutum. Single and multiple monosomics, trisomies and tetrasomics have been derived from G. hirsutum and its hybrids with the diploid species (Beasley and Brown, 1943; Brown, 1949). The salient features of these types will be described as a means of elucidating chromosome differentiation in Gossypium species and in G. hirsutum in particular.